1. Technical Field
The invention is related to skip-field video recorders wherein only alternate fields of an incoming video signal are recorded so as to reduce by a factor of two the amount of video tape required to record a given video program. More specifically, the invention is related to a skip-field video recorder particularly adept at recording images containing high-speed motion without creating objectionable artifacts in the playback video image.
2. Discussion Related to the Problem
Skip-field video recording is a technique well-known in the art, and is described, for example in U.S. Pat. Nos. 3,886,589, 3,882,539 and U.S. patent application Ser. No. 908,750, filed Sept. 18, 1986 by Hans-Peter Baumeister et al. and entitled "ZERO GUARD-BAND SKIP-FIELD VIDEO CASSETTE RECORDER" and in prior patents referred to in the Baumeister et al. patent application.
In typical skip-field video recorders of the prior art, only one video field of each video frame of the incoming video signal is recorded (for example, only the even field, or, only the odd field). Accordingly, the vertical sampling rate (image quality of objects moving in the field of view across horizontal video lines) is reduced by a factor of two. For very rapid motion, objectional artifacts may be visible in a playback image created from a skip-field video recording. This is particularly true of NTSC skip-field video recording of motion pictures, where the conversion from 24 frames per second to 30 frames per second is liable to create some odd artifacts under special conditions.
It would seem the only way to eliminate such problems would be to abandon the skip-field video recorder technique whenever it is desired to obtain high quality recording of video programs containing high-speed motion in the image. The disadvantage is that the amount of tape required to record a given program is doubled by abandoning the skip-field recording technique. Thus, there is a trade-off between recorded image quality and tape speed. The problem is how to perform skip-field video recording of high-speed images without increasing the risk of high-speed motion artifacts in the playback video image.